This application claims the priority of 101 17 401.2, filed in Germany, on Apr. 6, 2001 the disclosure of which is expressly incorporated by reference herein.
The invention relates to a fuel injection system for an internal-combustion engine having a fuel injector which is supplied with highly pressurized fuel by way of a high-pressure fuel line for injecting the fuel into the combustion space of the internal-combustion engine during an injection operation, and having a pressure control valve connected in front of the fuel injector in the high-pressure fuel line for controlling the pressure of the fuel injected during the injection operation.
For internal-combustion engines, particularly for diesel engines, fuel injection systems are known which contain a fuel injector, conventionally one of several, supplied by way of a high-pressure fuel line with highly pressurized fuel for the injection of the fuel into the combustion space of the internal-combustion engine during an injection operation. In addition, in the case of such a fuel injection system, a pressure control valve, which is connected in the high-pressure fuel line in front of the fuel injector, can be provided for controlling the pressure of the fuel injected during the injection operation into the combustion space of the internal-combustion engine.
Thus, from German Patent Document DE 197 34 354 A1, a fuel injection system for an internal-combustion engine of this type is known which has a pressure control valve for the time-dependent modulation of the fuel quantity injected during the injection operation. According to one of the embodiments described there, an adjusting device is provided for controlling this modulation valve, which adjusting device contains a piston acted upon by fuel on both sides. This piston controls a valve needle body of the modulation valve on the basis of a resulting force difference of the pressure forces acting on both sides of the piston. In this case, a first pressure space, which is acted upon by highly pressurized fuel in the opening direction of the modulation valve, is provided on the forward side of the piston acting on both sides, and, on the rearward side of the piston acting on both sides, a second pressure space is provided which is acted upon by fuel in the closing direction. During the displacement of the piston, which acts on both sides, in the sense of an opening of the modulation valve, the second pressure space is relieved from pressure by way of a discharge duct provided with a throttling point.
From German Patent Document DE 199 30 276 A1, an accumulator injection device of a similar type is known, in the case of which, a control valve is provided for the implementation of a second pressure level in the high-pressure fuel line supplying the fuel injector with highly pressurized fuel. When the control valve is closed, the fuel injector is supplied with a residual pressure which is maintained by means of a pressure-maintaining valve provided between the control valve and the fuel injector in the high-pressure fuel line.
It is an object of the invention to provide an improved fuel injection system which permits the shaping of the injection pressure distribution.
According to the invention, this object is achieved according to the invention by providing a fuel injection system for an internal-combustion diesel engine, having a fuel injector which is supplied with highly pressurized fuel by way of a high-pressure fuel line for injecting the fuel into the combustion space of the internal-combustion engine during an injection operation, and having a pressure control valve connected in front of the fuel injector in the high-pressure fuel line for controlling the pressure of the fuel injected during the injection operation, wherein the pressure control valve contains a freely displaceable piston operating on both sides and a slide connected into the flow path of the high-pressure control line for enlarging (opening) and reducing (closing) the passage cross-section of the flow path of the high-pressure fuel line as a function of the position of the piston, a first pressure space on the forward side of the piston which acts upon the piston in the opening direction of the slide, and a second pressure space on the rearward side of the piston which acts upon the piston in the closing direction of the slide, and wherein an adjusting valve is provided for adjusting the pressures in the first and/or second pressure space in the sense of a displacement of the piston in the opening or closing direction.
Advantageous further developments of preferred embodiments of the fuel injection system according to the invention are described herein and in the claims.
The invention provides a fuel injection system for an internal-combustion engine, particularly a diesel engine. The fuel injection system contains a fuel injector supplied by way of a high-pressure fuel line with highly pressurized fuel for the injection of fuel into the combustion space of the internal-combustion engine during an injection operation. Furthermore, a pressure control valve connected in front of the fuel injector in the high-pressure fuel line is provided for controlling the pressure of the fuel injected during the injection operation. According to the invention, the pressure control valve contains a freely displaceable piston, which operates on both sides, and a slide, which is connected into the flow path of the high-pressure fuel line, for the opening and closing of the passage cross-section of the flow path of the high-pressure fuel line as a function of the position of the piston. On the forward side of the piston, a first pressure space is constructed which acts upon the piston in the opening direction of the slide, and, on the rearward side of the piston, a second pressure space is constructed which acts upon the piston in the closing direction of the slide. An adjusting valve is provided for adjusting the pressures in the first and/or the second pressure space in the sense of a displacement of the piston in the opening or closing direction.
According to a preferred embodiment of the fuel injection system according to the invention, the first pressure space provided on the forward side of the piston is connected by way of a first flow connection with the upstream side of the high-pressure fuel line, and the second pressure space provided on the rearward side of the piston is connected by way of a second flow connection with the downstream side of the high-pressure fuel line.
Preferably the adjusting valve is provided for adjusting the pressure of the first pressure space.
According to a preferred embodiment, the adjusting valve is provided in a relief line connected to the first pressure space.
According to a particularly advantageous embodiment of the fuel injection system according to the invention, the adjusting valve comprises a proportional actuating device.
Such a proportional actuating device is particularly advantageously formed by a piezo actuator.
Preferably, an admission throttle is provided in the first flow connection connecting the first pressure space with the upstream side of the high-pressure fuel line.
Furthermore, it is an advantage for a damping throttle to be provided in the second flow connection connected with the downstream side of the high-pressure fuel line.
According to a particularly preferred embodiment of the invention, the second flow connection connecting the second pressure space provided on the rearward side of the piston with the downstream side of the high-pressure fuel line is constructed as a flow duct extending in the piston.
As an alternative, the second flow connection connecting the second pressure space provided on the rearward side of the piston can be connected as an exterior duct with the downstream side of the high-pressure fuel line.
The slide is preferably constructed in one piece with the piston, the first and the second pressure spaces being provided at the ends of the piston, and the slide being provided in a center region of the piston.
In the last-mentioned embodiment, it is particularly advantageous for the flow path of the high-pressure fuel line to form a transverse connection through the center region of the piston.
According to a preferred embodiment of the invention, it is provided that the flow duct forming the second flow connection extends in the longitudinal direction of the piston from the second pressure space to the transverse connection forming the flow path of the high-pressure fuel line.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.